Plastic article having flame retardant properties

ABSTRACT

New plastic articles are disclosed and claimed having flame retardant properties which contain a core of a plastic polymeric material (thermoplastic, thermoset, rigid foam or semi-flexible foam polymeric material) which is coated with a protective, flame retardant layer comprising a mixture of a thermoplastic polymeric material and a flame retardant, char-forming, intumescent system. The new articles are suitable for the manufacture of e.g. rods, beams, pipes, hoses, non-tubular profiles and panels which are useful in various industries such as the building, automotive and mining industries.

This is a CONTINUATION of application Ser. No. 07/835,151, filed Feb.13, 1992 now U.S. Pat. No. 5,413,828.

This invention relates to a plastic article having flame retardantproperties, in particular to an article containing a polymeric materialcoated with a protective, flame retardant polymeric layer whichcomprises an intumescent system.

Each year many fatal accidents and huge damages to private propertiesand industrial installations are caused by fire. This is particularlythe case where plastic articles are involved, because many plasticarticles are highly flammable, generate dense, toxic and corrosive smokewhen burning, rapidly lose their mechanical strength under the effect ofheat, and easily propagate fire through dripping.

To remedy this situation there is a general market demand as well as asteadily increasing legislation towards the use of fire resistant orflame retardant plastic articles in houses and in industry, for examplein applications such as e.g. frames, pipes, electrical cable hoses,insulation coatings and insulation panels.

The term plastic material used herein refers to thermoplastic polymericmaterial, to thermoset polymeric material as well as to polymeric rigidfoam and semi-flexible foam material. The term plastic article refers toan article the core of which is made from the said plastic material.

Various techniques have been developed to impart flame retardancy orfire resistancy to plastic articles. These techniques are based on theknowledge that certain materials are not combustible and/or are capableon their own or in combination with other compounds to impart flameretardant or fire resistant properties to materials which have been usedin connection with such compounds or combinations of compounds. Theterms fire resistant (FR) and flame retardant (FR) are used hereininterchangeably. The term FR materials refers to materials which havebeen used in connection with, or treated or modified by means of certainchemical compounds or mixtures of compounds (systems) to show reducedcombustion rate compared to the corresponding non-treated ornon-modified materials. Similarly the terms FR agent and FR system referto a chemical compound, respectively mixture of compounds, which impartsto the material which has been used in connection with or treated ormodified with the FR agent or FR system, a reduced combustion ratecompared to the corresponding non-treated or non-modified material.

A typical way to impart FR properties to plastic articles consists inthe manufacture of the articles from plastic materials which haveinherent FR properties. Such FR plastic materials contain halogen atomsor various other functional groups, e.g. phthalimide groups, whichprovide FR properties to the plastic material. The most widespreadinherent FR plastic material is polyvinyl chloride. Non-halogencontaining inherent FR plastic materials have, for various reasons, notgained widespread application.

Another way to render plastic articles flame retardant consists inpreparing the articles from a mixture of a flammable plastic materialand a FR agent, FR system or flame retardant, intumescent (FRI) system.

A typical group of FR agents comprises mono- and poly-halogenatedcompounds having a high content of halogens, usually chlorine and/orbromine, fluorine being used to a lesser extent. These FR agents can below-molecular weight compounds as well as high-molecular weight,polymeric materials. A further group of FR agents comprises phosphoruscontaining compounds, such as e.g. derivatives of phosphoric acid andpolyphosphoric acid. Another widely used group of FR agents comprisesmetal derivatives, such as e.g. hydrated alumina, magnesium hydroxide,calcium carbonate and, in particular, antimony salts. Furthermorenon-flammable fillers may be added to the mixture, such as mineralfillers. These various FR agents can be used alone or in combinationwith each other.

In spite of a significant reduction of flammability of the plasticarticles obtained by the above techniques, such approaches showconsiderable weaknesses. A major weakness relates to the reduction inphysical and mechanical properties of the plastic material due to thepresence of the FR agent, FR system or non-flammable filler. A furtherdisadvantage of plastic articles containing halogenated organiccompounds and/or certain metal derivatives, particularly antimonycompounds, relates to the fact that these articles generate dense andtoxic smokes upon exposure to fire. Another important disadvantage ofthese articles relates to the fact that they rapidly lose mechanicalproperties when they are exposed to excessive heat. The terms excessiveheat and heat are used herein interchangeably.

Still a further group of FR agents comprises FRI system, i.e. systemswhich have flame retardant, char-forming and intumescent properties. Aplastic mass containing a flame retardant, char-forming and intumescent(FRI) system will under the effect of heat (fire) expand to form anon-flammable, multi-cellular layer of a char-foam which provides anefficient shielding and insulation for the underlaying material againstdirect contact with fire and oxygen, as well as against heat transfer.

The requirements for flame retardant, char-forming, intumescent systemsare well known: these FRI systems contain three components:

(i) a catalyst, usually phosphoric or polyphosphoric acid, which ispresent in the form of a non-corrosive acid precursor which under theaction of heat is transformed into a phosphorus acid; the latterinitiates/catalyses the intumescent reaction;

(ii) a char-former, also referred to as carbonific compound, which is anorganic compound which under the action of the phosphorus acid and heatis transformed into a char;

(iii) a blowing agent which under the effect of heat and/or the catalystevolves non-flammable gases which can promote char-foam formation whilethe char is formed.

By appropriate selection of the components, efficient FRI system can beobtained which are free of halogen and undesirable metal derivatives,and which can be tailored as to the temperature at which the FRI systembecomes active. In some FRI systems two components, e.g. the char-formerand the blowing agent, are combined in a single chemical compound.

This approach also has significant weaknesses. The main disadvantage ofan article made from a mixture of a plastic material and a FRI systemresides in the fact that the presence of the FRI system can adverselyaffect the mechanical properties of the plastic material. Furthermorethis approach requires the use of considerable amounts of FRI system andis thus a quite expensive way to impart flame retardancy to articlesmade from plastic material.

A further way to impart FR properties to plastic articles consists in asurface treatment of the article including the application of a FR orFRI paint layer which is generally applied onto the article by means ofa brush, a roller or a spray. However these paint layers are not verysatisfactory because they present one or more of the followingdisadvantages:

they contain halogenated compounds and/or undesirable metal derivatives,

the adhesion of the paint layers onto plastic articles is oftenunsatisfactorily,

the paint layers are subject to mechanical damage during installationand handling of the article,

when exposed to water or a humid atmosphere, compounds present in thepaint layer such as e.g. phosphorus compounds may hydrolyse and/or maybe leached out,

under the influence of various factors the paint layer may peel off,leaving parts of the plastic article unprotected.

It is an object of this invention to provide a plastic article made fromflammable plastic material, having effective flame retardant propertieswhile substantially maintaining, upon exposure to fire its mechanicalproperties.

It is another object of this invention to provide a method for themanufacture of a plastic article having effective flame retardantproperties.

It is a particular object of this invention to provide a plastic pipehaving effective flame retardant properties which can be used in miningapplications in lieu of e.g. cast iron pipes.

In one aspect, this invention relates to a plastic article havingeffective flame retardant properties which contains a core of plasticmaterial which is coated with a protective, flame retardant polymericlayer, the layer comprising a thermoplastic polymeric material whichcontains a flame retardant, char-forming, intumescent system(hereinafter referred to as FRI system and FRI layer, respectively).

In a preferred aspect, this invention relates to a plastic articlehaving effective flame retardant properties which contains a core ofplastic material which is coated with a protective, flame retardantthermoplastic polymeric layer which comprises a polyolefin and a FRIsystem.

The plastic material forming the core can be any thermoplasticpolymeric, thermoset polymeric, rigid-foam or semi-flexible foampolymeric material, which materials may be reinforced or not. Suitablethermoplastic materials are, for example, polyethylene, polypropylene,polystyrene, acrylonitrile-butadiene-styrene copolymers,poly-alpha-methyl-styrene, polyvinyl chloride, poly-(meth)acrylates,poly-acrylonitrile, polyamides, polycarbonates, and any blends of two ormore thermoplastic polymers. Suitable thermoset polymeric materialsinclude, for example, epoxy resins, polyurethanes, high-hardness rubber,phenolic resins, and cross-linked polyesters. Suitable rigid-foam andsemi-flexible foam polymeric materials include, for example, phenolicfoams, polyurethane foams and polystyrene foams.

Reinforcement of the plastic materials may be achieved in conventionalmanner, for example by means of mineral fillers and/or fibrousmaterials, such as e.g. talc, clays, glass-fibers, carbon-fibers,mineral fibrous material, plastic fibers, textile fibers or metalfilaments. The fibrous material may be used in the form of continuousstrands, woven or non-woven or meshed sheets or randomly distributedchopped fibers. The surfaces of these fibrous reinforcement materialsmay furthermore be treated in a conventional manner to improve adhesionbetween the fibrous material and the plastic material.

The core material may furthermore contain conventional additives used inthe art, such as e.g. plasticisers and anti-oxidants.

The core may exist in a wide variety of forms. Typical forms are forexample rods, beams, pipes, hoses, non-tubular profiles and panels. Thecore shall be coated with the polymeric layer at least at the surface orsurfaces which may become directly exposed to fire and/or heat;preferably the core shall be coated at the complete outer and/or innersurface.

The most appropriate nature and grade of the plastic material and ofpossibly present reinforcement material, as well as the form andthickness of the core, may vary widely from article to article, and canbe defined by the skilled person in conventional manners having regardto the intended use of the article.

In one preferred aspect, the invention relates to a plastic article thecore of which comprises a thermoplastic polymeric material.

In another preferred aspect the invention relates to a plastic articlewith a core comprising a thermoset polymeric material.

In a further preferred aspect the invention relates to a plastic articlethe core of which comprises a rigid-foam polymeric material or asemi-flexible foam polymeric material.

The protective FRI layer according to the invention may comprise anythermoplastic polymeric material. In a preferred embodiment thethermoplastic polymeric material is halogen-free. In another preferredembodiment the thermoplastic polymeric material comprises a polyolefin.Particularly suitable materials are, for example, polyethylene, HDPE,LDPE, polypropylene, EVA (ethylene vinyl acetate), ethylene hexenecopolymers, any mixture thereof, and any mixture with otherthermoplastic polymeric materials. If the core comprises a thermoplasticpolymeric material, the FRI layer may comprise the same or a differentthermoplastic polymeric material.

The FRI polymeric layer may furthermore contain conventional additivesused in the art such as e.g. UV-stabilisers, colouring agents, pigments,anti-oxidants and plasticisers.

While various flame retardant, char-forming, intumescent systems (FRIsystems) are known, not all of them are appropriate for use according tothe invention. Suitable FRI systems have (i) to be compatible with thethermoplastic polymeric material of the layer, (ii) to be thermallystable under the processing conditions, and (iii) provide efficientflame retardancy. The selection of appropriate FRI systems can be madebased on publicly available product information and/or routineexperiments having inter alia regard to the conditions under which theFRI system shall be active and the FR requirements imposed to thearticle.

Preferred FRI systems according to this invention contain a phosphoricacid precursor and/or a polyphosphoric acid precursor as catalyst,preferably an ammonium phosphate and/or ammonium polyphosphate (APP).APP is particularly suited as catalyst for FRI systems in polymericmaterials containing a polyolefin, in particular polyethylene,polypropylene or any mixture thereof.

Protective polymeric layers containing only a mixture of APP and athermoplastic polymeric material (APP acting herein as catalyst andblowing agent and the polymeric material acting as char-former) presentacceptable FR properties but poor char-foam forming properties. FRIlayers containing an FRI system composed of APP, melamine andpentaerythritol, provide improved flame-retardant properties topolymeric layers but also present undesirable technical weaknessesresulting from the fact that melamine and pentaerythritol often do notdisperse well in thermoplastic polymers and polymer mixtures and cancause processing problems.

Preferred FRI layers for use according to the invention comprise FRIsystems containing APP and a synergist. The term synergist used hereinrefers to a single compound which acts both as a char-forming agent andas a blowing agent. These two-component FRI systems are preferred overthree-component FRI-systems because the APP-synergist system oftenpresents much better compatibility with the thermoplastic polymericmaterial than three component mixtures of separate catalysts,char-formers and blowing agents do. Various compounds may be used assynergists provided they are compatible with the APP and thethermoplastic polymeric material and provided they do not have anadverse effect on the processed FRI layer such as surface blooming,plate-out effects and decomposition or discoloration at the temperaturesrequired for processing of the polymeric layer. The suitability ofsynergist compounds in a certain thermoplastic polymer or polymermixture can be determined by the skilled person based on routineexperiments. Preferred synergists are compounds which are halogen-free.Typical synergists are for example oligomeric triazinilpiperazinecompounds, silicone fluids, isocyanurates, e.g. triglycidyliso-cyanurate(TGIC) and tris (hydroxyethyl) isocyanurate (THEIC).

The ratio of the components of a FRI system has to be balanced to obtainan optimal effect. The amount of each component of the FRI systemdepends on various factors including the nature of the catalyst,char-forming agent, blowing agent, or synergist, the nature of thepolymeric material and the degree of intumescency and flame retardancydesired. Suitable to optimal ratio of the components of the FRI system,as well as of the ratio FRI system to thermoplastic polymeric materialin the FRI layer, can be determined by the skilled person throughroutine experiments.

FRI systems according to this invention advantageously consist of,expressed by reference to the said FRI system being 100%, from 5% to 50%weight of FRI additive and from 95% to 50% weight of APP and/or ammoniumphosphate, preferably from 20% to 50% by weight of FRI additive and from80% to 50% by weight of APP and/or ammonium phosphate, more preferablyfrom 25% to 40% by weight of FRI additive and from 75% to 60% by weightof APP. By FRI additive is meant herein the synergist or a mixture ofthe char-forming agent and the blowing agent.

In typical FRI layers according to the invention the thermoplasticpolymeric material, which is preferably a polyolefin, represents from95% to 40% by weight and the FRI system from 5% to 60% by weightexpressed to the layer (100%). In a preferred embodiment thethermoplastic polymeric material represents from 80% to 50% weight andthe FRI system from 20% to 50% weight of the polymeric layer (100%). Thethickness of the polymeric layer to be used to impart effectiveflame-retardancy depends on the nature of the FRI system the weightratio FRI system/thermoplastic polymeric material in the layer, and thedegree of intumescency and flame retardancy desired. The thickness canbe defined by the skilled person on the basis of routine experiments.

For many applications a relatively thin FRI layer providing a goodheight and quality of intumescency is sufficient to impart adequateflame retardant properties to the plastic article.

The following are examples of FRI layer compositions, of compoundingprocesses for the manufacture of FRI layers and of flame retardantthermoplastic polymeric FRI layer material.

EXAMPLE 1

Components:

Thermoplastic polymer: polypropylene (a)

FRI system: mixture of ammonium polyphosphate (b) and oligomerictriazinilpiperazine derivative (c)

FRI system composition: weight ratio (b):(c) approx. 2:1

a) General compounding procedure:

Approximately 1250 g of a polymer (a)/FRI system powder mixture is addedto a Banbury mixer at 55-65° C. The batch temperature is increased to155-160° C. and maintained for 4 to 6 minutes. Care is taken not toexceed 200° C. The batch is removed from the mixer, cooled and groundinto chips. A second pass, using similar conditions, may be required ifpowder losses are significant during the first pass (e.g., if unmixedpowder exceeds 10-20 g), or if dispersion is inadequate.

Specimens of appropriate dimensions for testing flame retardancy andphysical properties result from conventional injection molding attemperatures of 210-215° C.

b) Specific example (FRI system load: 20% wt): Sample 1:

According to the above general procedure the following sample is made:

1000 g polypropylene (a) and 250 g FRI system were added to a BanburyMixer at 50° C. The batch temperature was increased to 150° C. in oneminute using a rotation of 77 rpm. Rotation was stepped up, asnecessary, to maintain this temperature for an additional five minutes.The batch was removed from the mixed, partially cooled, chopped using abench hydraulic guillotine and ground into chips.

Injection-molded test specimens were made in a conventional manner underthe following conditions: barrel and nozzle temperatures were 210-215°C.; injection pressure was 12,066 KPa (1750 psi). The final compositionof the resulting FRI layer material (Sample 1) was 80% by weightpolypropylene, 20% by weight total FRI system.

(a) Himont PRO-FAX 6524: Trademark of Himont USA, Inc.

(b) Phos-Chek P/40: Trademark of Monsanto Company

(c) Spinflam SPINFLAM MF82/PP: Trademark of Ausimont Group, MontedisonSpA

EXAMPLE 2

Components:

Thermoplastic polymer: polypropylene (a)

FRI system:

ammonium polyphosphate (b)

SFR-100 Silicone fluid (d)

pentaerythritol (e)

FRI system composition: weight ratio (b):(d):(e) approx. 3:1:1

a) General compounding procedure:

Using a Banbury Mixer, two passes are required. The first pass is madeat 150-165° C. without the silicone-based additive (d) in the mixture.The ground material from the first pass is added back to the mixer andheated to about 170° C., then SFR-100 silicone fluid (d) is added, andmixing is continued at 170° C. for an additional 4 to 6 minutes.

The batch is removed from the mixer, cooled, chopped, ground into chipsand injection molded as described in example 1.

b) Specific example (FRI system load: 25% wt): Sample 2:

937.5 g polypropylene (a), 187.5 g ammonium polyphosphate (b) and 62.5 gpentaerythritol (e), were mixed in a Banbury mixer at 150-165° C. forfour minutes, followed by cooling and grinding.

In a second pass, chips from the first pass were heated to 170° C. infour minutes, at which time 62.5 g of silicone fluid (d) was added. Themixture was mixed for an additional four minutes at 170° C. followed bycooling, grinding and injection molding as described in example 1.

The resulting FRI-layer material (Sample 2) had a final composition of75% polypropylene (a), 15% ammonium polyphosphate (b), 5% silicone fluid(d) and 5% pentaerythritol (e).

(a) Himont PRO-FAX 6524: Trademark of Himont USA, Inc.

(b) Phos-Chek P/40: Trademark of Monsanto Company.

(d) SFR-100 Silicone fluid: Trademark of GE Silicones, GeneralElectrics.

(e) PE-200 pentaerythritol, technical grade: Hercules Inc./Aqualon

EXAMPLE 3

Physical properties measured on injection molded samples preparedaccording to examples 1 and 2 are given below in Table 1.

                  TABLE 1                                                         ______________________________________                                        Physical properties of injection molded FRI layer samples                     FLAME RETARDANT                                                                            ASTM     PP resin                                                PROPERTIES   METHOD   (a)      Sample 1                                                                             Sample 2                                ______________________________________                                        UL 94 Flame Class                                                                          --       Burn     V-0    V-0                                     (1/16")                                                                       Oxygen Index (%)                                                                           D 2863   18.7     32.5   28.1                                    PHYSICAL                                                                      PROPERTIES                                                                    Specific gravity                                                                           D 792    0.88     0.97   0.99                                    Tensile properties                                                                         D 638                                                            Tensile strength (psi)                                                        Yield                 4,827    4,315  3,555                                   Break                 1,965    3,272  2,267                                   Elongation (%)                                                                Break                 7.9      2.3    11.2                                    Izod Impact Strength                                                                       D 256                                                            Notched (ft-lb/in)    2.0      0.2                                            Unnotched (ft-lb/in)  12.3     4.3    7.8                                     Melt Flow (g/10 min.)                                                                      D 1238   4.0      3.2    6.2                                     ______________________________________                                         (a) Polypropylene resin (PROFAX 6524: Trademark of Himont USA, Inc).          comparative sample/data.                                                 

EXAMPLE 4

Components:

Thermoplastic polymer: LDPE (low density polyethylene) (f)

FRI system:

ammonium polyphosphate (b)

oligomeric triazinilpiperazine derivative (c)

FRI system composition: weight ratio (b):(c) is approx 2:1

a) General compounding procedure:

Approximately 1250 g polymer (f)/FRI system powder mixture are mixed ina Banbury mixer at 100° C. The batch temperature is increased to150-160° C. and maintained for five minutes. Care is taken not to exceed177° C. The batch is removed from the mixer, cooled and ground intochips. A second pass, using similar conditions, may be required ifpowder losses are significant during the first pass (e.g., if unmixedpowder exceeds 10-20 g), or if dispersion is inadequate.

Specimens of appropriate dimensions for testing flame retardancy andphysical properties are injection molded at temperatures of about 182°C.

b) Specific example (FRI system load: 30%): Sample 3:

According to the above general procedure the following sample is made:

875 g of LDPE (f) and 375 g of FRI system were added to a Banbury Mixerat 100° C. The FRI system blend consisted of approximately 2:1 ammoniumpolyphosphate (b): synergist (c). The batch temperature was increased to154° C. in 3 to 5 minutes using a rotation of 77 rpm. Rotation wasstepped up, as necessary, to maintain this temperature for an additionalfive minutes. The batch was removed from the mixer, partially cooled,chopped using a bench hydraulic guillotine and ground into chips with agrinder.

Injection-molded test specimens were made in a conventional way underthe following conditions: barrel and nozzle temperatures were 170° C.and 230° C., respectively; injection pressure was 12,066 KPa (1750 psi).The final composition of the resulting FRI layer material (Sample 3) was70% LDPE, 30% FRI system.

(b) PHOS-CHEK P/40: Trademark of Monsanto Company

(c) SPINFLAM MF82/PE: Trademark of Ausimont Group, Montedison SpA.

(f) Grade LDPE 779, Dow Chemical Co.

Physical properties measured on sample 3 are given in Table 2.

                  TABLE 2                                                         ______________________________________                                        Physical properties of injection molded FRI layer sample 3                    FLAME RETARDANT                                                                              ASTM                                                           PROPERTIES     METHOD    LDPE (f)  Sample 3                                   ______________________________________                                        UL 94 Flame Class (1/16")                                                                    --        Burn      V-0                                        Oxygen Index (%)                                                                             D 2863    18.8      35.6                                       Smoke Optical Density                                                                        E 662                                                          Flaming Mode             52                                                   Nonflaming Mode          257       73                                         PHYSICAL PROPERTIES                                                           Specific gravity                                                                             D 792     0.92      1.06                                       Tensile properties                                                                           D 638                                                          Tensile strength (psi)                                                        Yield                    1,550     1,420                                      Break                    1,410     1,395                                      Elongation (%)                                                                Yield                    105       15                                         Break                    140       45                                         Izod Impact Strength                                                                         D 256                                                          Notched (ft-lb/in)       NB*       2.0                                        Unnotched (ft-lb/in)     NB*       12.0                                       Melt Flow, g/10 min.                                                                         D 1238    6.4       4.4                                        ______________________________________                                         (f) low density polyethylene LDPE Grade 779, Dow Chemical Co. comparative     sample/data.                                                                  *NB: sample not broken                                                   

EXAMPLE 5

In Table 3 samples of FRI layer material are presented which have beenprepared by conventional techniques in accordance with the proceduredescribed in Example 4.

In Table 4 physical properties are presented measured on injectionmolded specimen of Samples 4 to 7.

                  TABLE 3                                                         ______________________________________                                        Samples of compounded FRI layer material                                                   FRI System                                                       Thermoplastic  % weight load                                                                            % weight of components                              Sample N°                                                                     polymer     in FRI layer                                                                             APP (b)                                                                              synergist (c)                            ______________________________________                                        4      HDPE (g)    30         69.2   30.8                                     5      HDPE (g)    40         69.2   30.8                                     6      HDPE (h)    30         69.2   30.8                                     7      HDPE (h)    40         69.2   30.8                                     ______________________________________                                         (g) HDPE (3 MFI): Alathon 7030 (Du Pont Company)                              (h) HDPE (0.5 MFI): Alathon 585D (Du Pont Company)                            (b) ammonium polyphosphate (PhosCheck ® P/40: Monsanto Company)           (c) triazinilpiperazine derivative Spinflam ® MF82 Ausimont SpA)     

                                      TABLE 4                                     __________________________________________________________________________    Physical properties of typical injection molded FRI layer material                       ASTM    HDPE           HDPE                                        Property   Method                                                                            Units                                                                             MFI 3 (g)                                                                          Sample 4                                                                           Sample 5                                                                           MFI 0.5 (h)                                                                         Sample 6                                                                           Sample 7                         __________________________________________________________________________    Meltflow Condition (L)                                                                   D-1238                                                                            g/10                                                                              2.8  1.74 1.51 1.43  0.380                                                                              0.386                                           min                                                            Density    D-792                                                                             g/cc                                                                              0.96 1.08 1.14 1.16  1.08 1.13                             Tensile strength                                                                         D-638                                                                             psi 4200 2900 2800 2900  3009 3000                             Ultimate (2"/min)                                                             Elongation (2"/min)                                                                      D-638                                                                             %   900  165  20   13.7  69   56                               Gardner Impact                                                                           --  in-lb                                                                             --   71   18   12    50   17                               Resistance                                                                    Notched Izod R.T.                                                                        D-256                                                                             ft-lbs/in                                                                         1.89 1.12 0.887                                                                              1.35  2.64 2.33                             Flexural Modulus R.T.                                                                    D-790                                                                             1000.                                                                             222  180  250  276   200  250                                             psi                                                            UL 94 test (1/8")                                                                        UL94                                                                              --  --   V-0  V-0        V-0  V-0                              (1/16")                 V-0  V-0        V-2  V-0                              Oxygen Index   %        31.8 37.2       31.0 36.2                             Moisture before drying                                                                       %        0.80 1.14 4.2   2.51 6.61                             Moisture after drying                                                                        %        0.14 0.16 0.77  0.19 0.31                             __________________________________________________________________________     (g) HDPE (3 MFI): Alathon 7030 (Du Pont Company); comparative sample/data     (h) HDPE (0.5 MFI): Alathon 5850 (Du Pont Company); comparative               sample/data                                                              

In a preferred aspect this invention relates to plastic pipes havingflame retardant properties, having a core made of polymeric materialwhich is coated with an outer protective, flame retardant thermoplasticpolymeric layer which comprises a polyolefin, a mixture of polyolefins,or a mixture of a polyolefinic material with any other thermoplasticpolymeric material, and a flame retardant, char-forming, intumescentsystem. Pipes according to the invention may have various inner andouter diameters and they are very suitable for various applications inindustry and in houses, for example for use under humid conditions inmines as conducts for air and water.

In another preferred aspect this invention relates to flame-retardant,non-tubular plastic profiles, having a core from a polymeric materialwith a protective polymeric layer having flame-retardant properties andcomprising a thermoplastic polymeric material containing a flameretardant, char-forming, intumescent sytem.

The profiles are very suitable for the manufacture of frames for variousapplications, e.g. frames for windows and doors for the buildingindustry.

In still another preferred aspect this invention relates to plastichoses having flame retardant properties having a core made of apolymeric material which is coated at the inner side or at the inner andouter side with a protective, polymeric layer having flame retardantproperties, the polymeric layer comprising a thermoplastic polymericmaterial containing a flame retardant, char-forming intumescent system.

Such hoses may be of particular interest for housing electrical wires inbuildings, in the automotive industry and in special equipment.

The core of the pipe, frame or hose may optionally be reinforced by anysuitable material known in the art such as, for example, fibers, choppedfibers, networks, meshed, woven or non-woven sheets from compatiblematerials like glass fibers, carbon fibers, mineral fibers, textilefibers, fibers from polymeric materials and metal filaments. Thepolymeric material forming the core may be a halogen containing polymer,e.g. PVC, although halogen-free polymers are preferred. Typicallypreferred polymers are polyethylene, HDPE, LDPE, propylene, and anymixtures thereof. The polymeric material may furthermore contain one ormore other thermoplastic polymers, such as e.g. polycarbonates,polyamides and polyesters, provided they are compatible with thepolymeric material.

The thermoplastic polymeric material of the protective FRI layer of suchpipes, non-tubular profiles and hoses corresponds to the one describedherein before.

Plastic articles, according to the invention having a protective FRIlayer, in particular pipes, hoses and non-tubular profiles, can bemanufactured at relatively low cost according to known techniques andwith conventional equipment. For example, the pipes, hoses andnon-tubular profiles according to the invention can be made by extrusionsuch as sequential extrusion, co-extrusion, crosshead-extrusion, and byjacketing.

The flame retardant plastic articles according to the invention presentmany advantages over conventional flame retardant articles made frominherently flame retardant halogen containing polymers, or from polymersor polymer blends mixed with FR or FRI systems. The advantages include:

minimal amounts of FRI system are required to impart effectiveflame-retardancy to plastic articles; this enables to manufacture thearticles at reduced material cost;

possibility to manufacture flame-retardant plastic articles free ofhalogens and undesirable metal derivatives;

quality FRI chars are formed when the article is exposed to fire orexcessive heat providing efficient shielding against fire, against firepropagation via dripping and against heat transfer;

the articles do not evolve dense and toxic smoke or corrosive combustiongases under fire conditions, or the generation thereof is at leastsignificantly retarded and/or reduced by the char-foam layer formed;

the protective layer containing the FRI system is a thermoplasticpolymeric layer which readily resists to mechanical damage;

the FRI layer can be applied simultaneously or consecutively during themanufacture of the article before installation of the latter whichensures a homogenous, high-quality protective layer;

the FRI layer does not adversely interfere with the physical andmechanical properties of the core of the article;

the ease of connecting FR articles according to the invention, e.g.pipes and non-tubular profiles, by conventional techniques withoutcausing much damage to the FRI layer over larger surfaces;

the flame-retardancy can be tailor made to a certain extent byadaptation of the nature of the FRI system, the ratio of FRI system tothermoplastic polymeric material in the FRI layer, and the thickness ofthe FRI layer.

The manufacture of typical articles according to the invention isexamplified below.

EXAMPLE 6

Flame Retardant Laminated Sheets:

Components:

Thermoplastic polymer: HDPE (i)

FRI system: mixture of ammonium polyphosphate (b) and oligomerictriazinilpiperazine derivative (c)

FRI system composition: weight ratio (b):(c) approx. 2:1

FRI layer composition:

Formulation A: weight ratio HDPE:FRI system is 60:40

Formulation B: weight ratio HDPE:FRI system is 70:30

Formulation C: weight ratio HDPE:FRI system is 75:25

(i): HDPE:ELTEX TUB 121 Trademark of Solvay Company

(b): Phos-Chek P/40: Trademark of Monsanto Company

(c): Spinflam MF82/PE (without APP) Trademark of Ausimont SpA

The FRI layer material formulations A, B and C were compounded inconventional way as described in example 4.

Laminated sheet samples were prepared by conventional coextrusion of aFRI layer on a 4 mm thick sheet of unmodified HDPE (i) containing carbonblack, as follows:

Sample 8: FRI formulation A; FRI layer thickness 1 mm

Sample 9: FRI formulation A; FRI layer thickness 2 mm

Sample 10: FRI formulation B; FRI layer thickness 1 mm

Sample 11: FRI formulation B; FRI layer thickness 2 mm

Sample 12: FRI formulation C; FRI layer thickness 1 mm

Sample 13: FRI formulation C; FRI layer thickness 2 mm

In a standard set up plaques of these samples in horizontal positionwere exposed with the FRI layer to a bunsen burner flame (flametemperature about 1100° C.) for 2 to 3 minutes whilst observing thesample and whilst measuring via a thermocouple the temperature at theback of the sample. The test results are summarised in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Flame retardancy presented by laminated sheet samples                                                    Back temp (° C.)                                                                 Time to                                  Sample FRI System                                                                              FRI layer after 2 min.                                                                            softening                                n°                                                                            % wt*     mm**      exposure  (min)                                    ______________________________________                                         8     40        1         122.5     2.7                                       9     40        2         105       3.25                                     10     30        1         150       2.25                                     11     30        2         108       3                                        12     25        1         170       2                                        13     25        2         120       3                                          14***                                                                               0        0         200       <1.5                                     ______________________________________                                         *weight load (%) of FRI system in FRI layer                                   **thickness of FRI layer                                                      ***comparative sample/data                                               

EXAMPLE 7

Flame Retardant Laminated Sheets

Through conventional extrusion comparative samples were made of sheetsof HDPE (i) and HDPE (i) containing a FRI system, and, also throughconventional coextrusion, samples of flame retardant laminated sheetsaccording to the invention were made as follows:

the FRI system is ammonium polyphosphate (b) and oligomerictriazinilpiperazine derivative (c) in the weight ratio 2:1.

the thermoplast in the core and in the FRI layer is the same, i.e. HDPE(Eltex Tub 121: Solvay Company).

    ______________________________________                                                  FRI-layer Composition                                                                      Thickness of                                           Sample          HDPE     FRI system                                                                            sample in mm                                 N°                                                                            Core     % wt     % wt    Core  FRI layer                              ______________________________________                                        15*    HDPE     --       --      3     --                                     16*    --       60       40      --    3                                      17*    --       75       25      --    3                                      18     HDPE     75       25      4     1                                      19     HDPE     60       40      4     1                                      20     HDPE     60       40      4     3                                      ______________________________________                                         *Comparative sample/data                                                 

In a standard set up plaques of these samples in vertical position wereexposed with the FRI layer, if available, to an intensive flame of apropane/butane torch and the changes to the plaques were observed. Theresults are summarised below:

Sample 15:

after 1 min 47: flames are visible at the backside

after 2 min the burner is removed:

the fire is self-supporting.

Sample 16:

a char structure is formed

after 2 min the burner is removed:

no flames are visible at the backside

the sample is slightly deformed but its form is still intact,

the sample is auto-extinguishing.

Sample 17:

a char structure is formed

after 1 min 55 the burner is removed:

no flames are visible at the backside

the sample starts dripping.

Sample 18:

a char-foam structure is formed

after 2 min the burner is removed:

no flames are visible at the backside

the sample is auto-extinguishing

the sample is not deformed.

Sample 19:

idem as for sample 19

Sample 20:

a char-foam structure is formed

after 6 min of exposure the burner is removed

the sample is auto-extinguishing

the sample is not deformed.

EXAMPLE 8

Flame Retardant Plastic Pipe

A flame retardant plastic pipe according to the invention was madeaccording to the following particulars:

FRI system composition: ammonium polyphosphate (b) and oligomerictriazinilpiperazine derivative (c) in a weight ratio of 2:1;

FRI layer composition: thermoplastic polymer HDPE (j) 70% by weight andFRI system 30% by weight (expressed to the total weight (100%) of thethermoplastic polymer plus the FRI sytem); in addition 1 part of carbonblack per hundred parts of thermoplastic polymer plus FRI system wasadded to the composition.

The FRI layer material was compounded in a conventional way. A sample ofthe compounded material passed the UL94 (1/16"; 1.5 mm) and UL94 (1/8";3.2 mm) flame test (result V-0).

Core material: HDPE (j)

(b) Phos-Check® P/40: Monsanto Company

(c) Spinflam® MF82: Ausimont SpA

(j) HDPE: mixture, having a melt flow in dex (MFI) of 1.3, of Alathon®7030 and Alathon® 5850 (Alathon® trademark of Du Pont Company).

According to standard co-extrusion techniques a flame retardant plasticpipe according to the invention was made. Two single screw extruderswere used for the co-extrusion. The polymeric material was predried atabout 76° C. for 1.5 hours. The system was started up using the sameHDPE polymer in both extruders. Once a consistent pipe was obtained theFRI layer material was fed to the extruder providing the FRI layer ofthe pipe. The working temperatures were for the extruder providing theFRI layer about 193° C. and for the extruder providing the core about177° C. The pipe had an outer diameter of 110 mm, an inner diameter of80 mm and a FRI layer of 2.5 mm thickness.

A sample of about 30 cm length of the obtained flame retardant pipe(sample 21) was subjected to a flammability test as follows: the samplewas exposed to an intense flame from a propane torch for 2 to 3 minutes.Periodically the flame was removed and the flame retardancy of thesample was visually inspected. The results are given below in Table 6.

                  TABLE 6                                                         ______________________________________                                        Flame retardant properties of HDPE pipe sample 21                             Phenomenon inspected                                                                              Results                                                   ______________________________________                                        deformation of the article                                                                        no                                                        fusion of the article                                                                             no                                                        inflammation of the article                                                                       no                                                        dripping            no                                                        hole burned in the pipe                                                                           no                                                        outer char-foam layer formed                                                                      yes                                                       ______________________________________                                    

The above results clearly show the flame retardant properties and thetechnical advantages of a flame retardant plastic pipe according to theinvention.

Another aspect of the invention relates to structural laminates havingflame retardant properties and their manufacture. These laminates have acore of rigid-foam or semi-flexible foam which is coated with a layer ofa flame retardant, thermoplastic polymeric material containing a FRIsystem. The layer may be coating one or both major sides of the laminateand optionally also one or more of the er ect ing s ide surfaces.Typical examples of such laminates are rigid-foam and semi-flexible foampanels which are suitable for use as insulation panels in variousapplication, e.g. in the building industry, and in the automativeindustry.

The laminates can be manufactured by conventional techniques and fromconventional foam-forming compositions, as, for example, described inthe patents GB 1,197,221; U.S. Pat. No. 4,165,413; U.S. Pat. No.4,292,363; GB 1,580,565; U.S. Pat. No. 4,438,166; U.S. Pat. No.4,028,158; U.S. Pat. No. 3,166,454; U.S. Pat. No. 3,874,980; U.S. Pat.No. 4,073,997; U.S. Pat. No. 4,764,420; U.S. Pat. No. 4,221,555; EP0,118,013; EP 0,146,012 and EP 0,066,967. To manufacture laminatesaccording to the invention, the flame retardant, thermoplastic polymericlayer with the FRI system is applied, according to the processesdescribed in the said patents, either as the facing sheet material,replacing the facing sheet material used in the described processes, or,provided adequate adhesion is ensured, in addition and at the outer sideof the described facing sheet material.

Compounded FRI layer material may not be flexible enough to enable itsrolling up to larger rolls of FRI layer sheets. It is understood that ifthis is the case the FRI layer sheet to be used as facing sheet for thelaminates may be made by conventional extrusion either previously,followed by its cutting into pieces of sheet having the desireddimensions, or as a first step of a continuous process for themanufacturing of flame retardant laminates.

The core material can be any polymeric rigid-foam or semi-flexible foam,preferable a polymeric rigid-foam, which optionally may containconventional reinforcement materials. Typical foam materials are forexample phenolic foams, polyisocyanate foams, polyurethane foams,polystyrene foams and PVC foams. Typical reinforcement materials are forexample glassfibers, carbon fibers, metal filaments, mineral fibers,plastic fibers, and textile fibers, strands of glassfibers, choppedglassfibers, meshed, woven and non-woven sheets or mats of glassfibers,metal gauzes and wire netting.

What is claimed is:
 1. A flame retardant plastic article consistingessentially of a core of plastic polymeric material having coatedthereon a protective, flame retardant layer, the protective flameretardant layer consisting essentially of (i) a thermoplastic polymericmaterial selected from the group consisting of a polyolefin and blendsof polyolefins and (ii) a flame retardant, char-forming, intumescentsystem containing a flame retardant, char-forming, intumescent additiveand a catalyst selected from the group consisting of a phosphoric acidprecursor, a polyphosphoric acid precursor, and combinations of thephosphoric acid precursor and the polyphosphoric acid precursor.
 2. Theplastic article according to claim 1 wherein the plastic polymericmaterial of the core comprises a thermoplastic polymeric material. 3.The plastic article according to claim 1 wherein the plastic polymericmaterial of the core comprises a thermoset polymeric material.
 4. Theplastic article according to claim 1 wherein the plastic polymericmaterial of the core comprises a rigid foam or semi-flexible foampolymeric material.
 5. The plastic article according to claim 1 whereinthe plastic polymeric material of the core further comprises areinforcement material.
 6. The plastic article according to claim 1wherein the thermoplastic polymeric material of the protective, flameretardant layer is halogen-free.
 7. The plastic article according toclaim 1 wherein the polyolefin is selected from the group consisting ofpolyethylene, HDPE, LDPE, polypropylene, and any mixture thereof.
 8. Theplastic article according to any one of claims 1-3, 5-6, and 7 whereinthe article is a pipe.
 9. The plastic article according to any one ofclaims 1-3, 5-6, and 7 wherein the article exhibits a non-tubularprofile.
 10. The plastic article according to any one of claims 4-6 and7 wherein the article is a laminate.